(1) Field of the Invention
The present invention relates to low temperature-fired porcelain articles having a low dielectric constant and a high quality coefficient Q, and to electronic parts using such porcelain articles.
(2) Related Art Statement
In the high frequency circuit radio instruments such as cellular phones, top filters, interstage filters, local filters, etc. are used as high frequency circuit filters, and a laminated type dielectric filter is used as an interstage filter. An example of such a laminated type dielectric filter is disclosed in JP-A 5-243,810.
In order to produce the dielectric-laminated filter, a plurality of green sheets are produced from a powdery ceramic material to constitute a dielectric, a given electrode pattern is formed on each of the green sheets by printing with a given conductive paste. Then, a laminate is obtained by laminating the resulting green sheets, and the laminate is fired so that the conductive paste layers and the green sheets are simultaneously fired to densify the laminate.
At that time a metallic conductor having a low melting point, such as a silver-based conductor, a copper-based conductor or a nickel-based conductor is generally used as the electrode, their melting points are not more than 1,100xc2x0 C., for example, and sometimes as low as around 930xc2x0 C. For this reason, the dielectric needs to be sintered at a firing temperature lower than the low melting point metal constituting the electrode.
In order to decrease stray capacity, shorten the delay time and reduce the high frequency loss of an oscillator and a condenser housed, it is desired that the low temperature-fired porcelain article has a decreased dielectric constant ∈r and an increased quality coefficient Q. However, low temperature-fired porcelain articles having the optimum fired temperature of not more than 1,000xc2x0 C., a dielectric constant of not more than 10, a quality coefficient Q of not less than 2500, and an absolute value of a temperature coefficient xcfx84f of the resonance frequency of not more than 30 ppm/xc2x0C. have not been available.
For example, in order to provide a low temperature-fired porcelain article capable of being fired at a low temperature and having a wide optimum firing temperature range, a high insulating resistance and a low dielectric constant ∈r, JP-B 7-98,679 proposes a low temperature-fired porcelain article containing an aluminum component in an amount of 2.0 to 10.0 wt % when calculated as Al2O3, a barium component in an amount of 20.0 to 50.0 wt % when calculated as BaCO3, a silicon component in an amount of 40 to 70 wt % when calculated as SiO2, a boron component in an amount of 1.0 to 3.0 wt % when calculated as B2O3, a chromium component in an amount of 0.3 to 3.0 wt % when calculated as Cr2O3, and a calcium component in an amount of 0.3 to 3.0 wt % when calculated as CaCO3. However, no measure has been recognized to control the quality coefficient Q of the low temperature-fired porcelain to not less than 2500, and porcelain articles which can be fired at optimum firing temperatures of not more than 1,000xc2x0 C. have not been realized.
On the other hand, alumina and a glass-epoxy compound are used as materials for multi-layer wired substrates with low dielectric constants.
The present inventors have tried to incorporate condensers or inductors in multi-layer wired substrates made of materials having low dielectric constants. However, since the temperature coefficient xcfx84f of the resonance frequency of alumina or glass-epoxy compounded substrates is less than xe2x88x9260 ppm/xc2x0 C., the alumina substrates or the glass-epoxy compounded substrates could not be employed for the condensers or the inductors requiring temperature compensation with high accuracy. On the other hand, low temperature-fired, BaOxe2x80x94SiO2xe2x80x94Al2O3-based porcelain articles have their optimum firing temperatures of not more than 1,000xc2x0 C., porcelain articles having the dielectric constants of not more than 10 and the quality coefficient of not less than 2500 have not been offered. In addition, no examination has been made upon xcfx84f.
In order to provide low temperature-fired porcelain articles which enable low temperature firing with a wide optimum firing temperature range and possess high insulation resistance and low dielectric constants, for example, JP-B 7-98,679 proposes a low temperature-fired porcelain article that contains 2.0 to 10.0 wt % of an aluminum component when calculated as Al2O3, 20.0 to 50.0 wt % of a barium component when calculated as BaCO3, 40.0 to 70.0 wt % of a silicon component when calculated as SiO2, 1.0 to 3.0 wt % of a boron component when calculated as B2O3, 0.3 to 3.0 wt % of a chromium component when calculated as Cr2O3, and 0.3 to 3.0 wt % of a calcium component when calculated as CaCO3. However, a method has not been recognized to control the quality coefficient Q of the low temperature-fired porcelain article to not less than 2500. Further, a porcelain article which has the quality coefficient Q of not less than 2500 and which can be fired at an optimum firing temperature of not more than 950xc2x0 C. has not been realized. Furthermore, a method has not been described to lessen an absolute value of the temperature coefficient xcfx84f of the resonance frequency of the low temperature-fired porcelain article.
It is an object of a first aspect of the present invention to provide a low temperature-fired BaOxe2x80x94SiO2xe2x80x94Al2O3 based porcelain article having a dielectric constant of not more than 10 and a quality coefficient Q of 2,500. The quality coefficient Q is measured by the Hakki-Coleman method.
The low temperature-fired porcelain article according to the first aspect of the present invention comprises a barium component in an amount of 40 to 65 wt % when calculated as BaO, a silicon component in an amount of 25 to 46 wt % when calculated as SiO2, an aluminum component in an amount of 0.1 to 20 wt % when calculated as Al2O3, a boron component in an amount of 0.3 to 1.5 wt % when calculated as B2O3, and a zinc component in an amount of 0.5 to 20 wt % when calculated as ZnO, wherein the porcelain article has a dielectric constant xcfx84r of not more than 10, and a quality coefficient Q of not less than 2500.
It is an object of a second aspect of the present invention to provide a low temperature-fired, BaOxe2x80x94SiO2xe2x80x94Al2O3 based porcelain article having a dielectric constant ∈r of not more than 10, a quality constant of not less than is 2500 and an absolute value of a temperature coefficient xcfx84f of a resonance frequency of not more than 30 ppm/xc2x0C. with high strength.
The low temperature-fired porcelain article comprises a barium component in an amount of 40 to 65 wt % when calculated as BaO, a silicon component in an amount of 25 to 46 wt % when calculated as SiO2, an aluminum component in an amount of 0.2 to 20 wt % when calculated as Al2O3, a boron component in an amount of 0.3 to 1.5 wt % when calculated as B2O3, a chromium component in an amount of 0.5 to 3.5 wt % when calculated as Cr2O3, and a zinc component in an amount of 0.5 to 20 wt % when calculated as ZnO, wherein the porcelain article has a dielectric constant ∈r of not more than 10, a quality coefficient Q of not less than 2500 and an absolute value of a temperature coefficient f of a resonance frequency of not more than 30 ppm/xc2x0C.
The following description on the zinc component, the silicon component, the aluminum component, and the boron component is also applicable to the porcelain articles according to the first and second aspects of the present invention.
When the zinc component is incorporated in an amount of not less than 0.5 wt % as calculated in the form of ZnO, the coefficient of thermal expansion of the low temperature-fired article decreases, and can be easily sintered, which enables firing at a low temperature. When the zinc component is not more than 20 wt %, reduction in the quality coefficient Q can be prevented.
When the silicon component is incorporated in an amount of not less than 25 wt % as calculated in the form of SiO2, the dielectric constant ∈r can be controlled to not more than 10. When it is in an amount of not more than 46 wt %, the porcelain article can be fired at a low temperature.
When the aluminum component is incorporated in an amount of not less than 0.1 wt % (particularly preferably not less than 2) as calculated in the form of Al2O3, a celsian phase having high strength can be increased in the porcelain article, and the strength of a substrate made of such a porcelain article can be increased to 2,000 kg/cm2. When the content of the aluminum component is not more than 20 wt % (particularly preferably not more than 15 wt %), low temperature firing is possible.
When the boron component is incorporated in an amount of not more than 1.5 wt % (particularly preferably not more than 1.0 wt %) as calculated in the form of B2O3, the quality coefficient Q can be not less than 2,500. It has not been known that the quality coefficient Q of the porcelain article can be increased by decreasing the content of the boron component in the BaOxe2x80x94SiO2xe2x80x94Al2O2 based low temperature fired porcelain ceramic material like this, when the porcelain article can be obtained by firing at a low temperature. When the boron component is incorporated in an amount of not less than 0.3 wt % (particularly preferably not less than 0.5 wt %), the porcelain article can be obtained by firing at a low temperature.
When the chromium component is incorporated in an amount of not less than 0.5 wt % (particularly preferably not less than 1 wt % when calculated as Cr2O3), the temperature coefficient xcfx84f of the resonance frequency can be controlled to not more than 30 ppm/xc2x0C. and the optimum firing temperature for the low temperature-fired porcelain article can be decreased. When the chromium component is incorporated in an amount of not more than 3.5 wt % (particularly preferably not more than 2.5 wt % when calculated as Cr2O3), the temperature coefficient xcfx84f of the resonance frequency can be controlled to not more than 30 ppm/xc2x0C.
As mentioned above, the first aspect of the present invention succeeded in maintaining at a high level of not less than 2,500 the quality coefficient Q of the low temperature-fired porcelain having a low dielectric constant ∈r by incorporating the boron component and the zinc component in an appropriate combination of their addition amounts, while maintaining the sinterability at the low temperature.
As mentioned above, the second aspect of the present invention succeeded in maintaining at a high level of not less than 2,500 the quality coefficient Q of the low temperature-fired porcelain having a low dielectric constant ∈r by incorporating the boron component, the chromium component and the zinc component in an appropriate combination of their addition amounts and also in decreasing the absolute value of the temperature coefficient xcfx84f of the resonance frequency to not more than 30 ppm/xc2x0C., while maintaining the sinterability at the low temperature.
Further, according to the low temperature-fired porcelain articles of the first and second aspects of the present invention, mainly the addition of the zinc component decreases the coefficient of thermal expansion of the porcelain article, and makes the firing shrinkage factor in a temperature range of 500 to 800xc2x0 C. close to that of a low temperature-fired porcelain article having a higher dielectric constant ∈r. As a result, if a laminate is obtained by laminating a green sheet to produce the low temperature-fired porcelain article according to any one of the first and second aspects of the present invention as a first low dielectric constant layer and a second green sheet to produce another low temperature-fired porcelain article having a dielectric constant of 10 to 150 higher than that of the first layer, and a joint body is obtained by firing the laminate, the resulting substrate fired is free from warping and peeling at a joining interface.
Therefore, a second object of the present invention is to provide an electronic part comprising a first low dielectric constant layer made of the low temperature-fired porcelain article according to anyone of the first and second aspects of the present invention, and a second dielectric layer joined to the first dielectric layer, wherein the second dielectric layer has a dielectric constant ∈r of 10 to 150 which is larger than that of the first layer. The ∈r of 10 to 150 means that the electronic part has a large condenser capacity, that a wavelength-shortening effect of the resonance frequency is large and that xcfx84f may be smaller than 30 ppm/xc2x0C.
As the low temperature-fired porcelain article constituting the second dielectric layer, the following are particularly preferable.
BaOxe2x80x94TiO2xe2x80x94ZnOxe2x80x94SiO2xe2x80x94B2O3 
BaOxe2x80x94TiO2xe2x80x94Bi2O3xe2x80x94Nd2O3xe2x80x94ZnOxe2x80x94SiO2xe2x80x94B2O3 
BaOxe2x80x94TiO2xe2x80x94Bi2O3xe2x80x94La2O3xe2x80x94Sm2O3xe2x80x94ZnOxe2x80x94SiO2xe2x80x94B2O3 
MgOxe2x80x94CaOxe2x80x94TiO2xe2x80x94ZnOxe2x80x94Al2O3xe2x80x94SiO2xe2x80x94B2O3 
The electronic parts targeted by the present invention are not particularly limited, but laminated dielectric filters, multi-layered circuit boards, dielectric antennas, dielectric couplers, dielectric composite modules, etc. are recited by way of example.
These and other objects, features and advantages of the invention will be appreciated upon reading of the following description of the invention, with the understanding that some modifications, variations and changes could be made by the skilled person in the art to which the invention pertains.
In the following, the first aspect of the present invention will be explained in more detail.
In order to produce the low temperature-fired porcelain article according to the present invention, it is preferable that starting materials for the respective reagents are mixed in a given ratio to obtain a mixed powder, the mixed powder is calcined at 1,000 to 1,200xc2x0 C., the resulting calcined powder is crushed to obtain a ceramic powder. Preferably, a green sheet is formed by using the ceramic powder and a glass powder composed of SiO2, B2O3 and ZnO, and the green sheet is fired at 850 to 930xc2x0 C. As the starting materials for the respective metallic oxide components, an oxide, a nitrate, a carbonate, a sulfate or the like of each of the metals may be used.